It seems unlikely, Garmin is a very engineering led company. At least it was when I worked there 10 years ago!
Part of that engineering focus is an insane attention to the BOM, and to support(call center) and warranty (returns & repairs) costs. I think both of these things make it unlikely that Garmin will add a cellular modem to start tracking otherwise unconnected devices.
Interesting. It surprises me how BAD most of Garmin's software is. They regularly break syncing functionality for weeks at a time. Sometimes watches need reboots to figure out how to sync to a phone. The sunrise/sunset graph on my $600 watch has NEVER been right.
You can push activities to your Garmin account but they don't bother engineering in any additional functionality, eg, to show your last activity if uploaded from outside, or to account for externally uploaded activities in your training metrics. It never feels like they're interested in improving the functionality of existing devices.
Don't get me wrong, I'm happier with my Forerunner 945 than I was with my Apple Watch, but only just. Basically, it does enough things that my Apple Watch can't do, to make suffering with the majority of things it's somewhat worse at, worthwhile as a tradeoff.
I think they're hardware engineering focused, not software engineering.
Hence your Forerunner 945 will last most of a week (minus gas-enabled exercise time), where your Apple Watch goes about 2 days at most.
Garmin does already sell one smart watch containing an LTE cellular modem and is supposed to release another one later this year. LTE is an extra cost option, like with the Apple watch.
Part of that engineering focus is an insane attention to the BOM, and to support(call center) and warranty (returns & repairs) costs. I think both of these things make it unlikely that Garmin will add a cellular modem to start tracking otherwise unconnected devices.